Process of and apparatus for conserving gas material



PROCESS OF AND APPARATUS FOR CONSERVID IG GAS MATERIAL Filed June 20,1941 2 Sheets-Sheet 1 INVENTORS EDWARD E YENDALL HENRY C. KORNEMANN June8, 1943.

E. F. YENDALL ET AL PROCESS OF AND APPARATUS FOR CONSERVING GAS MATERIALFiled June 20, 1941 2 Sheets-Sheet 2 nun INVENTORS" EDWARD E YENDALLHENRY c. KORNEMANN Patented June 8, 1943 2,321,445 PROCESS OF ANDAPPARATUS FOR CON- SERVING GAS MATERIAL Edward F. Yendall and Henry C.Kornemann,

Kenmore, N. Y., assignors Products Company,

to The Linde Air a corporation of Ohio Application June 20, 1941, SerialNo. 398,908 19 Claims. (Cl. 62-1 This invention relates to a processofand apparatus for conserving a commercially valuable gas material inthe liquid state, such gas material having a boiling point atatmospheric pressure below 273 K. The invention relates moreparticularly to a process of and apparatus for conserving liquid oxygenproduced by the lowtemperature rectification of air.

Liquid oxygen is customarily produced by the low-temperature separationof air including rectification in at least two stages. In such processthe air to be rectified is compressed to a suitable high pressure, freedof undesirable constituents such as moisture and carbon dioxide,refrigerated to relatively low temperatures, and partially liquefied bycountercurrent heat exchange with the nitrogen-containing product of theseparation. The cooled and partly liquefied air-is, in some cases,subjected to a preliminary treatment including washing of the vaporphase portions with the liquid phase portions before it is passed intothe first or higher pressure rectification stage. In the first stage ofrectification there is formed a liquid comprising more than 50% nitrogenand containing the major portion of the oxygen of the air and anotherfluid product comprising mainly nitrogen. Both these fiuid products ofthe first stage are expanded to the pressure of the last stage ofrectification and introduced at suitable portions of the last stage, thefluid containing mainly nitrogen being passed to the upper end of thelast rectification stage so that the Hiquid portion thereof provides areflux for the last stage. The liquid oxygen produced collects :'n andis withdrawn from the lower end of the last stage. It is customary tooperate the highpressure stage of rectification under a pressure ofabout '75 lbs. per square inch gauge and the last stage under a pressureof about to 10 lbs. per square inch gauge. The liquid oxygen producedthus has a temperature equal to its boiling point corresponding to thepressure of the last rectification stage.

The liquid oxygen customarily produced is of commercial purity andcontains about 99.6% oxygen, and unless otherwise specified the termliquid oxygen as used herein will refer to the liquid oxygen ofcommercial purity. The term fluid as employed herein is intended toinclude material in the liquid state, the gaseous state, or mixed liquidand gaseous states.-

When the liquid oxygen produced under a pressure of 5 to 10 lbs. persquare inch is transferred into a receiving vessel such as a wellinsulated storage tank and it is desired to maintain the liquid oxygenin such tank at substantially atmospheric pressure, an appreciableportion of the liquid produced will flash into vapor. The amount ofliquid flashed into vapor corresponds to the refrigeration required tocool the balance of the liquid to the boiling point temperature atatmospheric pressure. When the pressure drop is 8 lbs. per square inch,the amount of such loss may be about 4% of the liquid produced. It hasalso been proposed to operate the storage tank at substantially thepressure of the upper column and thus have available a pressure head fortransferring the liquid from the storage tanks into transport tankslocated at the same level as the storage tank. When such liquid istransferred into the transport tanks where it is to be held atatmospheric pressure, a portion of the liquid similarly flashes intovapor.

It has been proposed to save the gas so produced by compressing it intothe customary high-pressure oxygen cylinders or by compressing such gasand passing it into the air-separation apparatus at a suitable point.The first method of conserving the gas loss requires the use ofcompressing and cylinder handling machinery which is not alwaysavailable in a liquid producing plant and requires power for itsoperation, while the second method incurs the danger of contaminatingthe oxygen and interfering with the operation of the rectificationapparatus.

When liquid oxygen is stored at atmospheric pressure or is shipped ininsulated portable tanks under pressures substantially above atmosphericpressure, the normal unavoidable leakage of heat into such tanks causesa constant slow evaporation of some of the liquid which constitutes afurther liquid loss. In the case of the portable tanks, it has beennecessary to blow such gas to the atmosphere. It has been proposed tosubcool the liquid oxygen to a temperature substantially below itsboiling point at atmospheric pressure before it is put into the portabletanks so that the liquid can be maintained in the portable tanks for adesired period of time before heat leak will have warmed it to atemperature such that vaporization will continue after the maximumpressure to be maintained in the tank has been reached. Suchsub-cooling, however, has been accomplished by the evaporation of asubstantial portion of the liquid under a reduced pressure so as to coolthe rest of the liquid and this results in a reduction of the liquidoxygen that can be shipped from the plant.

It is a. principal object of the present invention to provide animproved process of and apparatus for conserving a liquefied gas productsuch as liquid oxygen produced by low-temperature separation of a gasmixture such as air, by subcooling such liquid product before it ispassed into the storage tank or receiving container. Other objects ofthe invention are to provide a process of and apparatus for sub-coolingliquid oxygen produced by the low-temperature rectification of air byeffecting heat exchange of the oxygen product with a suitablelow-temperature fluid drawn from the rectification stages; to controlthe degree of sub-cooling of the liquid oxygen by selecting the pointfrom which the cooling fluid is drawn from the rectification stages andby selecting the pressure to which such fluid is expanded; to furthercontrol the degree of sub-cooling by proportioning the amount of coolingfluid employed for sub-cooling the liquid oxygen to the amount of liquidoxygen to be sub-cooled; to efiect the sub-cooling of the liquid productby heat exchange with an expanded liquid drawn from the lower part of ahigher-pressure stage of rectification; to efiect the sub-cooling of theliquid product by heat exchange with a fluid removed from the upper partof a higher-pressure rectification stage to obtain deeper sub-cooling;for conserving any vapors generated in the receiving container byliquefying such vapors in heat exchange with a fluid drawn from therectification stages and expanded to a ferring liquid oxygen from onecontainer to another by gravity substantially without gas loss.

The above and other objects and novel features of the invention will beapparent from the following description taken with the accompanyingdrawings in which:

Fig. 1 is a sectional view schematically showing an exemplary apparatusfor carrying out the invention, including means for sub-cooling theoxygen product by liquid drawn from the lower end of the high-pressurerectification stage and showing a stationary storage tank and a portabletank arranged according to the invention;

Figs. 2 and 3 are sectional views schematically showing two alternativearrangements of the apparatus for sub-cooling the oxygen product byemploying a fluid drawn from the upper portion of the high-pressurestage; and,

Fig. 4 is a fragmentary sectional view of another portion of apparatuswhich may be employed in conjunction with the apparatus illustrated inFigs. 1, 2, and 3 for reliquefying vapors drawn from the tanks.

Referring now to the drawings, a two-stage air rectifying apparatus isillustrated generally at A. At B is generally indicated, a liquid oxygenstorage tank for receiving the product of the rectifying apparatus. At Cthere is indicated generally a portable tank such, for example, as arailroad tank car connected to receive a supply of liquid oxygen fromthe storage tank B or the rectifying apparatus; and at D (Fig. 4) isshown generally a device for reliquefying vapors drawn from the tanks Band C.

The customary apparatus for compressing and refrigerating air andpreparing it for admission to the rectifying apparatus A constitutes nopart of the present invention and is not shown in the interests ofcleamess of the drawings. The rectifying apparatus A may be of thecustomary type having a lower column or high-pressure stage l into whichthe compressed and partly liquefied air is introduced through a conduitIL The upper end of the column In is provided with a condenser l2surrounded by the liquid oxygen chamber l3 which forms the lower end ofthe lower pressure; and for trans- 0 upper column M. The lower column I0is provided with a liquid collecting shelf 45 arranged to receive aportion of the liquid produced by the condenser l2, such liquid beingthe result of the condensation of vapors passing from the upper end ofthe column l0 into the condenser l2. Part of the liquid produced by thecondenser l2 provides a reflux for the lower column so that the liquidcollected on the shelf l5 contains very little oxygen. Both upper andlower columns I4 and 10, respectively, are provided with suitable gasand liquid contact trays IS in the customary manner. To provide refluxfor the upper column M, the liquid collected by the shelf I5 istransferred to the upper end of the column M by a transfer conduit l1provided with an expansion valve IS. The nitrogen product of therectification in the upper column which contains but very little oxygenpasses out through the conduit l9 and the refrigeration containedtherein is employed to cool the incoming air. I

The oxygen product of the upper column which collects in the chamber I3is withdrawn therefrom through a conduit 20 at a suitable rate so as tomaintain a desired height of liquid in th chamber l3. It was previouslycustomary to pass the liquid withdrawn through conduit 20 directly tothe storage tank B by gravity flow, the tank B being positioned at a lowlevel. According to the invention, however, there is interposed in theliquid-oxygen discharge conduit, a heat exchanger indicated generally atH for sub-cooling the liquid. Such heat exchanger may have any suitableconstruction but is here shown as a chamber 2| having disposed therein aheat-exchange pipe coil 22, the conduit 20 connecting with the lower endof the pipe coil 22. The upper end of the pipe coil 22 and, at thatpoint there is interposed a control valve 24.

The lower end of the column I0 is provided with a liquid collecting sump25 in which is collected a liquid containing most of the oxygen of theair admixed with a large portion of liquid nitrogen. The proportion ofoxygen in such liquid is substantially greater than the proportion ofoxygen in air but the liquid still contains more than 50% nitrogen andis a liquid with a highnitrogen content. It was customary to pass suchliquid directly to the upper column for rectification therein. Accordingto one embodiment of the invention. however, the chamber 2| of the heatexchanger H is connected to the sump 25 by a conduit 26 controlled by anexpansion valve 21, and from the upper end of the chamber 2| a conduit28 conducts the fluid originating at the sump 25 into the upper columnII at an intermediate point thereof. If the upper column is operatedunder a pressure of about 8 lbs. per square inch gauge, the liquidoxygen collecting in the chamber l3 will be at its boiling point at suchpressure and have a temperature of 1'78 C. If such liquid oxygen werereduced to atmospheric pressure after passage through the valve 24,about 4% thereof would flash into vapor. However, if the lower column isoperating under a pressure of about 75 lbs. per square inch gauge, andthe upper column at about 8 lbs. per square inch gauge. a part of theliquid drawn from the sump 25 and passed through the expansion valve 21will flash into vapor and at the same time both the liquid and vaporwill have its temperature reduced to a temperature that may be as low as-189 C. The liquid oxygen passing through the coil 22 can therefore becooled to a temperature is connected to the discharge line 23,

approaching l89 C. Since the boiling point of liquid oxygen atatmospheric pressure is 183 C.. it will be seen that a substantialdegree of sub-cooling is attained and n flashing of liquid oxygen intovapor will occur due to the pressure reduction from 8 lbs. per squareinch gauge to the pressure of the storage tank B.

The storage tank B may be of the customary construction including aninner liquid-holding vessel 29 surrounded by an outer shell 36 andhaving a relatively thick layer of heat-insulating material 3| betweenthe vessel 29 and the shell 30. The tank B is preferably supported at asuitable elevation by a frame 32 and by columns 33 for mounting theshell 36 on the frame 32. The tank B is elevated sufficiently so thatliquid may be discharged by gravity to the portable containers C. Thedischarge line 23 which, like other portions of the apparatus and pipelines operating at low temperatures. is thoroughly heat insulated, isconnected with the bottom of the vessel 29 by a conduit 34.

The portable tank C may be a tank mounted on a vehicle such as a railwaycar 35. The construction of the portable tank C is generally similar tothe storage tank B and includes an inner vessel 36, anouter shell 31provided with braces 38 supporting it on the car 35 and a layer of heatinsulation 39 between the vessel and the shell. The tank C is alsoprovided with a liquid filling and discharging line 49 which isconnectable with the discharge line 23 by a flexible connector 4|. Stopvalves 42 and 43 are preferably provided adjacent either end of theflexible connection 4|. The tanks B and C are preferably also providedwith gas withdrawal connections 44 and 45 leading from the upperportions of the vessels 29 and 36, respectively, and connected togetherby a conduit 46, the conduit 46 being coupled to the connection 45 by aflexible connector 41. Stop valves 48 and 49 are provided adjacent theends of the connector 41. Theconduit 46 is also provided with a pressurerelief valve 50 which is adjusted to release gas on the attainment of anexcessive pressure in the tank B and a valved connection 46' that may beplaced intocommunication with a gas holder if it should be desired torelease gas to such holder to reduce the gas pressure in the systembelow that for which the safety valve 50 is set to operate.

In the event that the liquid in vessel 29 becomes warmed so that thepressure builds up to a pressure in excess of atmospheric pressure, orin the event that it is desired to recover gas contained in a portabletank C, gas may be withdrawn from the conduit 46 from either or bothtanks B and C through a connection controlled by a stop valve 52. Thegas withdrawn through 1 connection 5| may be conserved by reliquefyingif by heat exchange with a fluid drawn from the rectification, forexample, the gas may be liquetied in the liquefying device D illustratedin Fig. 4.

The liqucfying device D may be in the form of any suitableheat-exchanging device. A preferable form. however, comprises a liquidstorage vessel 53. which is surrounded by heat insulation contained inan outer casing 54. The cooling liquid is supplied to the vessel 53 fromany suitable point of the rectification pparatus A or from the airliquefying apparatus. A convenicnt source of cooling fluid is fromthesump 25 of the rectifying apparatus. A conduit 56 controlled by aregulating valve 56 is connected to the bottom of the lower column l6andarranged a heat exchanger 65 to to pass liquid from the "sump 25 intothe vessel 53. The vessel 53 is preferably operated under substantiallyatmospheric pressure and since the pressure in the lower column I6 issubstantial. it will be seen that a substantial head is available forthe transfer of such liquid. Hence, the vessel D may be-located at anysuitable position, such for example, as at the level of, or above thetank B. For convenience, the location is here shown as below the frame32.

Within the casing 54 is preferably located a gas-phase heat exchanger 51through which the conduit 5| passes. The heat exchanger 51 has passagessurrounding the conduit 5| for conducting the vapors discharged from thevessel 53 so as to effect heat exchange between such vapors and the gaspassing through the conduit 5|. A connection 58 conducts the vapors fromthe vessel 53 to the heat exchanger 5'! and a connection 59 dischargesthe vapors to the atmosphere. It will be observed, however, that ifdesirable, the vapors discharged through conduit 59 could be conductedto a suitable point of the rectifying apparatus. A heat-exchange coil 66is submerged within the liquid in the vessel 53 and has its upper endconnected with the conduit 5| and its lower end connected by a conduit6| to a pump 62. The discharge outlet of the pump 62 is connected by aconduit 63 to the discharge line 23. A stop valve 64 may be interposedin the conduit 63. By the pump 62 the liquid formed in the heat-exchangecoil 60 may be transferred back to the tank B. If the reliquefyingdevice D is placed .at a sufficient elevation, the pump 62 could beomitted and the liquid produced in the coil 66 could be arranged to flowto the tank B by gravity. In Figs. 1, 2, and 3 similar elements of theapparatus are designated by the same reference characters. Referringmore particularly to Fig. 2, the liquid oxygen produced and passedthrough the heat-exchange pipe coil 22 is sub-cooled by a fluid whichhas a very high nitrogen content. Such fluid is obtained by arrangingthe conduit I? which draws fluid including liquid from the shelf l5 ofthe lower column l6 to pass through cool it by heat exchange with thecold outflowing nitrogen product conducted to the heat exchanger 65through the conduit l9. The cooled shelf fluid is conducted by a conduit66 to the lower end of the heat-exchanger chamber 2| which is herepositioned at a higher level. Before entry into the chamber 2|, theshelf fluid passes through an expansion valve 61. From the upper end ofthe chamber 2|, the shelf fluid (liquid and gas) is passed to the upperend of the upper column l4 through the conduit 68. If desired, a portionof the shelf fluid may under special conditions be by-passed around theheat exchanger H through a by-pass conduit 69 connecting the conduit 66with the upper end of the column l4. Conduit 69 is likewise providedwith an expansion valve 10. In this form of the apparatus, the liquidcollecting in the sump 25 of the lower column is transferred directly tothe mid-portion of the upper column by transfer conduit 26' controlledby expansion valve 21.

Another arrangement for employing shelf liquid for sub-cooling the coil22 is illustrated in Fig. 3 in which such shelf liquid is directlyconducted by a by-pass conduit II into the chamber 2|, an expansionvalve 12 being provided at the entrance to the chamber 2|. The nitrogenefliuent from the column I4 is conducted by the conduit |9 through theheat exchanger 65 .from

of the upper column l4, the: conduit being controlled by an expansionvalve I6.

In Fig. 3, and in Fig. 2, when the by-pass conduit 69 is employed, theflow through the valves 6! and 12 may be restricted and controlled tomaintain a liquid level in the chambers 2| just sufficient to cover thecoils 22, the remainder of the shelf fluid being passed through theconduits 69 and [1. The maintenance of such liquid level is optional inthe apparatus of Fig. 2 but is preferable in the apparatus of Fig. 3 toinsure the passage of adequate reflux liquid to the column H. In theapparatus of Fig. 2, the heat exchanger 65 operates in the customarymanner for cooling the shelf fluid; a large amount of the gas-phaseportion of the shelf fluid may be liquefied, and the entire shelf fluidcooled due to the low temperature of the efiluent nitrogen leaving theupper column which, if the upper column pressure is 8 lbs. per squareinch gauge, will be about 192 C. This temperature will be attained bythe shelf fluid upon expansion through the valve 61 because theexpansion is to the same pressure. The heat exchanger 65 insures thatmore of the shelf fluid will be in the liquid state after expansion. Inthe apparatus of Fig. 3, the expansion of a portion of the shelf fluidthrough the valve 12 also reduces its temperature to 192 C. althoughthis temperature could be reduced still lower if the conduit I3 werearranged to discharge the vapor from chamber 2| to a portion of theapparatus operating at a lower pressure. By employing shelf fluid forsub-cooling, the temperature of the liquid oxygen, can readily bereduced to -190 C. and thus the liquid can be maintained in storage atthe plant or, if desired. during transportation for a considerableperiod of time before its temperature is raised by heat leakage to --183C., the boiling point at atmospheric pressure.

In the operation of the liquefier D, it will be evident that anysuitable liquid having a boiling point at or below 183 C. can beemployed in the vessel 53. Ordinarily such liquid is preferably takenfrom the sump of the rectifying apparatus and withdrawn at a relativelyslow rate so as not to disturb the operation of the rectifyingapparatus. In cases where air is washed with portions of liquid airbefore entry into the rectifying column for the elimination of certainimpurities, the liquid waste discharged to take away such impurities maybe passed into the ves- Sci 53. Also, various liquid wastes sometimesdischarged from various other portions of the rectifying apparatus canbe passed into the vessel 53. During periods when the rectifyingapparatus is shut down, the liquid stored in the vessel 53 will beavailable for effecting the reliquefaction of vapors from the storageand transport tanks. When the rectifying apparatus is in operation, theportions of sub-cooled liquid oxygen continuously added to the storagetank B, mix with the liquid in the tank to cool the same and thus thenormal heat leak is constantly being counteracted and the pressure inthe tank can be maintained at a low value.

The sub-cooling of the liquid oxygen and the reliquefaction of vaporsfrom the tanks represents a certain quantity of refrigeration taken fromthe rectifying apparatus and this must be balanced by addedrefrigeration work input which results in a slight increase in powercost. This increased power cost however is more than compensated for bythe increased liquid oxygen output that can be delivered to theconsumers. In order to disclose the broad principles of the invention,several embodiments thereof have been illustrated and described.Obviously certain features of the invention can be used independently ofothers and changes may be made in various parts of the apparatus withoutdeparting from the essential principles of the invention. For example,although the conservation and dispensing of liquid oxygen has beenspecifically described, the principles of the invention may be employedfor the conservation and dispensing of other commercially valuable gasmaterials in the liquid state.

We claim:

1. A process for conserving liquid oxygen produced by the rectificationof air at low temperatures which comprises withdrawing a liquid having asubstantial nitrogen content from the rectiflcation; expanding suchwithdrawn liquid to a lower pressure; and effecting heat exchangebetween such withdrawn and expanded liquid and said oxygen product ofthe rectification to sub-cool said product to a temperature which isabove the temperature of said expanded liquid and low enough to preventvaporization of said liquid oxygen when passed into a receivingcontainer.

2. A process for conserving liquid oxygen produced by the rectificationof air at low temperatures which comprises passing the liquid oxygenproduced by said rectification in heat exchange relation with a fluiddrawn from said rectification, said fluid having a temperature below theboiling point of liquid oxygen corresponding to its pressure when passedinto a receiving container controlling the rate of withdrawal of saidfluid to cool said liquid oxygen to a desired temperature sufficientlylow toprevent vaporization thereof in said receiving container; andconducting said fluid after said heat exchange to join the nitrogenproduct of said rectification.

3. A process for conserving oxygen produced by the low temperaturerectification of air in stages at successively lower pressures, saidoxygen product being produced in the last of said rectification stagesat a pressure slightly above atmospheric pressure, which processcomprises withdrawing a fluid having a substantial nitrogen content froma prior stage of the rectification; expanding such withdrawn fluid to atleast substantially the pressure of the last of said rectificationstages; passing said oxygen product in heat-exchanging relation withsaid expanded fluid to bring said oxygen product into the subcooledliquid state; and transferring such subcooled liquid oxygen into areceiving container. wherein it is held under a pressure below that ofsaid last stage of rectification.

4. A process for conserving liquid oxygen according to claim 3 in whichsaid fluid comprises change with the oxygen product, to a portion ofsaid last stage of rectification.

51 Process for conserving liquid oxygen according to claim 3 in whichsaid fluid comprises the product of the next to the last stage ofrectification having the least oxygen content, and which includes thestep of conducting said fluid after said heat exchange with the oxygenproduct to join the outflowing nitrogen product of said last stage ofrectification.

6. A process for conserving liquid oxygen produced by the lowtemperature rectification of air in stages at successively lowerpressures, said liquid oxygen being produced in the last of saidrectification stages at a pressure slightly above atmospheric pressure,which process comprises withdrawing a fluid having a substantialnitrogen content from a prior stage of the rectification; eifecting heatexchange between said fluid and the cold gaseous nitrogen product ofsaid last stage of rectification to cool said fluid; expanding suchwithdrawn cooled fluid to substantially the pressure of the last stageof rectification; passing said liquid oxygen in heat-exchanging relationwith said expanded fluid to sub-cool the oxygen; and transferring thesub-cooled liquid oxygen to a receiving container wherein it is heldunder a pressure below that of said last stage of rectification.

7. A process for conserving liquid oxygen produced by the lowtemperature rectification of air in stages at successively lowerpressures, said liquid oxygen being produced in the last of saidrectification stages at a pressure slightly above atmospheric pressure,which process comprises withdrawing a fluid having a substantialnitrogen content from a prior stage of the rectification; dividing saidfluid into two portions; expanding and passing one of said portions offluid to the last stage of rectification; expanding and completelyvaporizing the other portion of said fluid in heat-exchanging relationwith said liquid oxygen product of the last stage of rectification tosub-cool the same; and transferring such sub-cooled liquid oxygen to areceiving container wherein it is held under a relatively low pressure.

8. A process for conserving liquid oxygen according to claim 7 whichincludes the step of conducting the vapors resulting from said heatexchange of said fluid with the oxygen product to join the nitrogenproduct of said last stage of rectification.

9. A process for conserving liquid oxygen produced by thelow-temperature rectification of air in stages at successively lowerpressures, said liquid oxygen being produced in the last of saidrectification stages at a pressure slightly above atmospheric pressure,which process comprises withdrawing a fluid having a substantialnitrogen content from a prior stage of the rectification; expanding suchwithdrawn fluid to at least substantially the pressure of the last ofsaid recti fication stages; passing said liquid oxygen inheat-exchanging relation with said expanded fluid to sub-cool theoxygen; transferring the sub-cooled liquid oxygen to a receivingcontainer wherein it is held under a pressure below that of said laststage of rectification; withdrawing vapors from said receiving containerfrom above the liquid therein; subjecting such vapors to heat exchangewith another portion of fluid having a relatively high nitrogen contentdischarged from said rectification stages so as to liquefy' said vapors;and transferring the liquid resulting from said liquefaction to saidreceiving container.

10. Process for conserving liquid oxygen produced by the low temperaturerectification of air in two stages at successively lower pressures whichprocess comprises passing said liquid oxygen product into a receivingcontainer insulated from the effects of the surrounding temperatures;withdrawing vapors from said receiving container from above the liquidtherein; subjecting such vapors to heat exchange with a body of liquidhaving a substantial nitrogen content drawn from said rectification soas to vaporize a portion of said body of liquid and liquefy said vapors;and transferring the liquid oxygen so produced to said receivingcontainer.

11. A process for conserving a liquefied gas product resulting from thelow-temperature rectification of a gas mixture in stages at diflerentpressures, which process comprises withdrawing a fluid having asubstantial content of a lower boiling point component of said gasmixture from a stage of the rectification other than the lowest pressurestage; expanding such withdrawn fluid to at least substantially thepressure of the lowest of said rectification stages; bringing said gasproduct into heat-exchanging relation with said expanded withdrawn fluidto sub-cool said gas product; and passing said sub-cooled product into areceiving container wherein it is held in the liquid state at arelatively low pressure.

12. A process for conserving oxygen produced.

by the low-temperature rectification of air in stages at successivelylower pressures, said oxygen being produced in the last of saidrectification stages at a pressure slightly above atmospheric pressure,which process comprises withdrawing a fluid having a substantialnitrogen content from a prior stage of the rectification; expanding suchwithdrawn fluid to at least substantially the pressure of the last ofsaid rectification stages; effecting heat exchange between said expandedfluid and said oxygen product to cool the latter to a temperature suchthat it is entirely liquid and remains in the liquid state whentransferred to a receiver at a lower pressure; and transferring saidoxygen product to such receiving container for storage therein.

13. Apparatus for conserving liquid oxygen produced by a two-stageair-rectifying apparatus, said liquid oxygen being produced in the stageoperating at the lower pressure, comprising means for withdrawing afluid having a substantial nitrogen content from the higher-pressure.stage of said rectifying apparatus; means for expanding such fluid toat least substantially the pressure of the lower-pressure stage of saidrectifying apparatus; a heat exchanger arranged to eiiect heat exchangebetween said expanded fluid and the oxygen product of the rectifyinga-pparatus to sub-cool the same; a heat-insulated receiving container;and means for transferring said sub-cooled oxygen from said heatexchanger to said receiving container.

14. Apparatus for conserving liquid oxygen according to claim 13 inwhich said higher-pressure stage comprises a rectifying column having aliquid collecting sump at its lower end, and said fluid withdrawingmeans is connected to withdraw said fluid irom said sump.

15. Apparatus for conserving liquid oxygen according to claim 13 inwhich said higher-pressure stage comprises a rectifying column having aliquid collecting sump at its lower end, a condenser at its upper endcooled by boiling oxygen, and a shelf for collecting a substantialportion of the condensate produced by said condenser; and in 6 whichsaid fluid-withdrawing means is connected to withdraw said fluid fromsaid shelf.

16. Apparatus for conserving liquid oxygen according to claim 13 inwhich said higher-pressure stage comprises a rectifying column having aliquid-collecting sum-p at its lower end, and in which said apparatusincludes a heat-insulated vessel for holding a body of cold liquid;means for conducting portions of liquid from said sump to said vessel;means for withdrawing vapors from said receiving container and passingsuch vapors in heat-exchanging relation with the body of liquid in saidvessel to condense said vapors; and means for transferring liquidproduced by condensation of said vapors to said receiving container.

17. System for dispensing liquid oxygen produced by a two-stageair-rectifying apparatus, said liquid oxygen being produced in the stageoperating at the lower pressure, said system comprising an elevatedheat-insulated storage tank adapted to hold a supply of liquid oxygen;means for sub-cooling said liquid oxygen product of the rectifyingapparatus by heat exchange with a colder fluid drawn from saidrectifying apparatus; means for transferring such sub-cooled liquidoxygen to said storage tank under a pressure lower than that of saidlower-pressure rectification stage; a heat-insulated transport containerpositioned at a lever lower than that of said storage tank; and conduitmeans connecting the lower portion of said storage tank with saidtransport container for transferring liquid by gravity from the storagetank to the transport container to charge the same, whereby substantialflashing of liquid into gas is avoided.

18. Apparatus for conserving liquid oxygen produced in thelower-pressure stage of a two-stage air-rectifying apparatus whichcomprises means for withdrawing a fluid having a substantial nitrogencontent from the higher-pressure rectiflcation stage; means for passingsuch fluid in heat-exchanging relation with the cold nitrogen product ofsaid low-pressure stage to cool the same; means for expanding such fluidto at least substantially the pressure of the low-pressure stage; a heatexchanger arranged to effect heat exchange between said expanded fluidand the oxygen product of said rectiiying apparatus to sub-cool thesame; a heat-insulated receiving container; and means for transferringsaid subcooled oxygen from said heat exchanger to said receivingcontainer for storage therein at a relatively low pressure.

19. Apparatus for conserving liquid oxygen produced by the low-pressurestage of a two-stage air-rectifying apparatus which comprises means forwithdrawing a fluid having a substantial nitrogen content from thehigher-pressure stage of said rectification; means for conducting aportion of such fluid in heat-exchanging relation with the nitrogenproduct discharged from said lowpressure stage; means for expanding andintroducing such cooled portion of fluid into the upper end of said lowpressure stage; means for expanding the remaining portion of said fluidto the pressure of the nitrogen product of said lowpressure stage; aheat exchanger arranged to effect heat exchange between said expandedportion of fluid and the oxygen product of said lowpressure stage tosub-cool the same; a heat-insulated receiving container; means fortransferring said sub-cooled oxygen from said heat exchanger to saidreceiving container; and means for conducting the vapors of said fluidfrom said heat exchanger to join with the nitrogen product of saidlow-pressure stage.

EDWARD F. YENDALL. HENRY C. KORNEMANN.

